Valve stop changer tools are utilized extensively with gas distribution lines where it becomes necessary to change out a line valve without depressurizing the upstream service line in which the valve is contained. A physical requirement of such changer tools is that they be able to seal off the pipe upstream of the valve through the use of a radially expandable plug which must first be passed through the valve ports from the downstream side of the valve. After the changer tool has been properly positioned and expanded for sealing engagement with the interior surface of the pipe upstream of the valve, the valve can be removed and replaced and/or repaired as necessary.
The changer tools are generally custom designed by a valve manufacturer to accommodate the port geometries of a particular model valve. Accordingly, such tools are generally unsuitable for use with different valves. Obviously, the person who is working with the valves in the field would prefer to have a valve stop changer tool which is operable with various model valves. One such versatile tool is disclosed by Ralph Henry in U.S. Pat. No. 4,597,147. The Henry tool employs an elastomeric plug positioned between a pair of restraining ends with each of the restraining ends comprising a plurality of contiguous elements which are laterally slidable so that the retaining ends are operable to axially confine the plug while squeezing and radially expanding the plug. The entire plug assembly is sufficiently small to enable passage through a variety of valve ports without regard to the port geometry, while the expansion ratio of the tool is sufficient to achieve the required seal in the upstream pipe to enable the removal of the valve. However, the Henry tool requires a large number of parts, which increases manufacturing expense.
Problems have also been encountered with prior changer tools which utilize an expandable plug in that after the plug has been axially compressed and radially expanded to form a seal and the valve has been removed and then replaced, the axial expansion of the compressed plug upon release of the axial compression forces is not as rapid as desired for prompt removal of the changer tool.